Advances in semiconductor technology have facilitated the development of smaller and smaller integrated circuits over the past thirty years; presently, industry possesses adequate technology to fabricate computers, telephones, scanners and video cameras, which can fit within in the pahn of the hand. These devices also tend to be more affordable than their larger predecessors. The design of smaller and smaller integrated circuits has allowed these size reductions.
Conventionally, the integrated circuits are mounted to a carrier, the use of which facilitates testing of the integrated circuit prior to mounting to a printed circuit board (PCB). The use of a carrier also enables redistribution of the input and output connections to be more compatible with PCB technology, and replacement of defective integrated circuits following mounting.
Typically, the carrier is larger than the integrated circuit itself and together, the integrated circuit and carrier form a “package”, which is individually mounted to a PCB, which can mount many integrated circuits and have a number of off-board connections for connecting other PCBs.
As the size of the integrated circuit continues to decrease, however, it is increasingly difficult to obtain further reductions in package size by relying solely upon reductions in the size of the integrated circuit. To achieve further package size reductions, recent design efforts have been devoted toward space savings achieved by stacking integrated circuits vertically on top of one another, especially in connection with memory technology. These design efforts have generally focused on providing ever-increasing numbers of integrated circuits into a smaller and smaller space, to thereby enable design of even smaller computers, telephones, scanners, video cameras, and other electronic devices.
The design efforts devoted toward stacking integrated circuits typically employ a special carrier, which has wire leads that extend laterally from the package for mounting to a peripheral frame. The peripheral frame provides structural support for the packages, and also carries an electrical bus for connection to the individual wire leads of each package. The vertically stacked packages are then encapsulated to be made moisture resistant, and are eventually mounted as a single unit to the PCB.
For the space savings achieved, however, the recent design efforts have required a relatively labor intensive and costly assembly process between separate packages. In addition, because the integrated circuits generate heat during operation, one design consideration is the presence of structure, which permits heat to escape from within the stacked packages, for dissipation outside the frame, although such structure generally further adds to the cost and complexity of the assembly.
There exists a definite need for a three-dimensional integrated circuit assembly, useable for both memory integrated circuits and other integrated circuits that provides for easy and efficient assembly and electrical connection of the vertically stacked integrated circuits. Preferably, such an assembly should be very low-cost and be compatible with existing interconnects and PCB technology. Further still, such an assembly should include an efficient method of heat dissipation.
As electronic circuits become larger and more complex, increased efforts continue to be directed toward the goal of decreasing size of circuit packages. In some types of packages, many integrated circuits are mounted side by side in close proximity to one another on a multi-layered substrate so that adjacent integrated circuits may be connected to one another by means of connecting leads that extend in a number of different planes, thereby decreasing horizontal dimensions of the package at the expense of some increase in vertical dimension.
Integrated circuits have also been stacked vertically one upon another to provide decreased size, weight and power as compared to single integrated circuit or multiple horizontally aligned integrated circuit packaging. However, because of the large number of integrated circuit connecting pads, which may be in excess of four hundred on a single integrated circuit, it has been difficult for integrated circuit stacking to adequately provide interconnections from all of the integrated circuit pads to one another as desired, or to external circuitry.
In other integrated circuit stacking arrangements, interconnecting leads between integrated circuits on different levels are provided at the sides of the stack. Leads are routed from each integrated circuit connecting pad to the side of the stack, and interconnections are made in the form of vertical connectors or vertical buses that extend along the exterior sides of the stack. Because the vertical surface area of the sides of the stack is limited, the number of input/output connections between the integrated circuit connecting pads of the integrated circuits of a stack and connecting elements at the outside of the stack is itself severely limited. In prior integrated circuit stacks, connecting leads from the integrated circuit connecting pads have been routed to one side of the stack so as to most conveniently form the vertical interconnects between stack layers and connections. This has been accomplished by adding metallization or additional leads on the integrated circuit or using other connection techniques, such as tape automated bonding. These techniques require special processing of the integrated circuits or wafers and add considerable cost to the stacking process.
In conventional stacked package structures for area array packages, the top package normally has at least a package size to clear the bottom mold cap size with solder balls having a large diameter, as well as a large ball pitch size, arranged in the peripheral area. As a result, the unnecessary large package size may be required to match the bottom package footprint.
The electronic industry continues to seek products that are lighter, faster, smaller, multi-functional, more reliable and more cost-effective. In view of the ever-increasing need to save costs and improve efficiencies, it is more and more critical that answers be found to these problems.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.